本文選題：活塞熱負(fù)荷 + 內(nèi)冷油腔�。� 參考：《山東大學(xué)》2015年碩士論文

【摘要】：目前發(fā)動機(jī)正朝著高功率密度、高可靠性、低油耗以及低排放的方向發(fā)展,導(dǎo)致發(fā)動機(jī)熱負(fù)荷大幅度提高。而活塞作為發(fā)動機(jī)的關(guān)鍵零部件之一,其可靠性會直接影響發(fā)動機(jī)的整體性能,并且活塞的工作環(huán)境異常惡劣,在工作過程中活塞頂面始終受到高溫燃?xì)獾闹芷谛宰饔?所以活塞頂部往往承受很高的熱負(fù)荷。為了保證活塞能夠安全可靠的工作,必須對活塞進(jìn)行有效的冷卻,而活塞噴油強(qiáng)制振蕩冷卻是目前應(yīng)用最廣泛的冷卻方式,對活塞內(nèi)冷油腔中冷卻機(jī)油的流動與傳熱特性研究不僅能夠為內(nèi)冷油腔的優(yōu)化設(shè)計提供依據(jù),而且可以為活塞的熱負(fù)荷計算提供相對精確的傳熱邊界條件。本文以帶有內(nèi)冷油腔的某水平雙對置發(fā)動機(jī)活塞為研究對象,采用CFD數(shù)值模擬的方法對活塞內(nèi)冷油腔中冷卻機(jī)油的流動與傳熱特性進(jìn)行了分析,并通過試驗與數(shù)值模擬相結(jié)合的方法對不同轉(zhuǎn)速工況下活塞的溫度場進(jìn)行了研究,具體內(nèi)容包括：(1)選用VOF兩相流模型與動網(wǎng)格技術(shù)并利用CFD軟件對內(nèi)冷油腔中冷卻機(jī)油的流動傳熱特性進(jìn)行研究,模擬分析了發(fā)動機(jī)在某一特定工況下油腔壁面的瞬態(tài)機(jī)油分布情況、瞬態(tài)換熱系數(shù)分布情況,油腔不同壁面位置(上表面、中間內(nèi)側(cè)面、中間外側(cè)面、下表面)處的換熱系數(shù)、整個油腔的壁面換熱系數(shù)以及機(jī)油填充率隨曲軸轉(zhuǎn)角的瞬態(tài)變化趨勢,最后研究了壁面平均換熱系數(shù)在油腔圓周方向上的變化趨勢以及發(fā)動機(jī)轉(zhuǎn)速的改變對冷卻機(jī)油瞬態(tài)傳熱特性所產(chǎn)生的影響。(2)采用存儲式活塞測溫系統(tǒng)在整機(jī)試驗臺架上對活塞頂部五個關(guān)鍵位置處的溫度值進(jìn)行了測量,得到了測溫點處的溫度隨不同發(fā)動機(jī)工況變化的動態(tài)響應(yīng)曲線和各測點在穩(wěn)態(tài)工況運行時的溫度值,為研究活塞熱負(fù)荷以及更為精確地修正溫度場計算模型提供了依據(jù)。(3)采用GT-POWER軟件對發(fā)動機(jī)整機(jī)熱力循環(huán)過程進(jìn)行模擬,得到了各工況下活塞頂面瞬時換熱系數(shù)和瞬時溫度,然后結(jié)合經(jīng)驗公式確定活塞頂面的穩(wěn)態(tài)傳熱邊界條件；同時,根據(jù)內(nèi)冷油腔中冷卻機(jī)油的CFD模擬計算和經(jīng)驗公式確定活塞內(nèi)冷油腔和其余部位的傳熱邊界條件；最后利用ABAQUS有限元計算軟件對各工況下的溫度場進(jìn)行計算,并將各測點處的計算結(jié)果同試驗值進(jìn)行對比,發(fā)現(xiàn)最大誤差為8.0%,說明計算結(jié)果較為合理。(4)針對活塞在高轉(zhuǎn)速工況運行時活塞頂部溫度偏高這一問題,研究了不同發(fā)動機(jī)轉(zhuǎn)速與機(jī)油噴射壓力工況下內(nèi)冷油腔中冷卻機(jī)油的傳熱特性以及冷卻機(jī)油噴射壓力的改變對活塞溫度場的影響,發(fā)現(xiàn)通過提高噴油壓力能夠明顯降低活塞頂部和環(huán)槽處的溫度值,可以作為高功率密度發(fā)動機(jī)加強(qiáng)活塞冷卻的改進(jìn)方案。
[Abstract]:At present, the engine is developing towards the direction of high power density, high reliability, low fuel consumption and low emission. As one of the key parts of the engine, the reliability of the piston will directly affect the overall performance of the engine, and the working environment of the piston is abnormally bad, the top surface of the piston is always subjected to the periodic action of high temperature gas during the working process. So the top of the piston tends to bear a high thermal load. In order to ensure that the piston can work safely and reliably, it is necessary to cool the piston effectively, and the forced oscillation cooling of piston injection is the most widely used cooling method at present. The study on the flow and heat transfer characteristics of cooling oil in the piston inner cooling oil chamber can not only provide the basis for the optimization design of the inner cooling oil chamber, but also provide a relatively accurate heat transfer boundary condition for the calculation of the thermal load of the piston. In this paper, the flow and heat transfer characteristics of the cooling engine oil in the inner cooling oil chamber of the piston are analyzed by using CFD numerical simulation method, taking the piston of a horizontal double-contrast engine with an internal cooling oil chamber as the research object. The temperature field of the piston under different rotational speed conditions is studied by the combination of experiment and numerical simulation. The specific contents include: 1) selecting VOF two-phase flow model and dynamic grid technology and using CFD software to study the flow and heat transfer characteristics of cooling oil in the inner cooling oil chamber. The transient oil distribution, transient heat transfer coefficient and heat transfer coefficient at different wall positions (upper surface, middle inner side, middle outer side, lower surface) of the engine under a certain working condition are simulated and analyzed. The transient variation trend of wall heat transfer coefficient and oil filling rate with crankshaft angle of the whole oil chamber, Finally, the variation trend of wall average heat transfer coefficient in the circumferential direction of the oil chamber and the influence of the engine speed on the transient heat transfer characteristics of the cooling engine oil are studied. The temperature values at five key positions at the top of the piston were measured on the bench. The dynamic response curves of the temperature at the measuring points with different engine working conditions and the temperature values of the measured points in the steady state are obtained. In order to study the thermal load of piston and modify the model of temperature field more accurately, the thermal cycle process of engine is simulated by GT-POWER software, and the instantaneous heat transfer coefficient and instantaneous temperature of piston top surface are obtained under various working conditions. At the same time, according to the CFD simulation calculation and empirical formula, the heat transfer boundary conditions of the inner cooling oil chamber and other parts of the piston are determined. Finally, the temperature field under various working conditions is calculated by using ABAQUS finite element calculation software, and the calculated results at each measuring point are compared with the experimental values. It is found that the maximum error is 8.0, which shows that the calculation result is reasonable. (4) aiming at the problem that the top temperature of piston is on the high side when the piston is running at high rotational speed, The heat transfer characteristics of cooling engine oil in the cooling oil chamber under different engine speed and engine oil injection pressure and the influence of the cooling oil injection pressure on the piston temperature field are studied. It is found that by increasing the injection pressure, the temperature at the top of the piston and at the ring groove can be significantly reduced, which can be used as an improved scheme for enhancing the piston cooling of the high power density engine.
【學(xué)位授予單位】：山東大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：TK403

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